This invention relates to the fabrication of a small-scale structure and, more particularly, to the fabrication of a narrow pole tip in the write portion of a magnetic read/write head.
A read/write head of a computer hard disk or a magnetic recording tape is positioned closely adjacent to a recording medium, separated from the recording medium by an air bearing that does not allow them to touch or that permits only light touching. A data bit is written onto an area of the recording medium, typically a track moved past the read/write head, using the writing portion of the read/write head by locally changing the magnetic state of the recording medium. That magnetic state is later sensed by the read sensor to read the data. The write structure and the read structure are usually integrated together in the read/write head.
In the most popular design, the write structure includes a small-scale horseshoe-like electromagnet with the poles oriented perpendicular to the air bearing surface (ABS) that faces the air bearing. Because of the small size, the electromagnet, including the legs of the horseshoe, the pole layers, the magnetization coil, and the related structure, are fabricated by microelectronic techniques as a multilayered structure.
A continuing trend in the industry is to make the tracks in the recording medium ever narrower and more closely spaced, so that more information may be stored on the recording medium. In order to write onto a narrow track on the recording medium, the pole tip of one of the poles of the write head is made very narrow and has reached submicron widths in current writing devices. The fabrication of such a write pole tip presents some difficult challenges because of the geometries. The pole is deposited overlying the write structure. The pole tip is narrower than the pole, so that there is a flaring of the width of the pole material from the pole tip toward the pole. In some designs the flare is made quite pronounced and the location of the flare is close to the air bearing surface.
When the pole tip and pole are fabricated by conventional microelectronic techniques, the profile of the pole tip may be ragged near the location of the flare, a condition termed xe2x80x9cnotchingxe2x80x9d. Techniques such as the application of coatings to the underlying substrate are used to reduce the incidence of notching, but such techniques add more fabrication steps and are not fully satisfactory in the results achieved.
There is a need for an approach to minimize or avoid the notching of the pole tip in the writing portion of the read/write head. The present invention fulfills this need, and further provides related advantages.
The present invention provides a method for fabricating a projection structure such as a pole tip and pole of a magnetic read/write head, and a structure produced by the method. The projection structure does not suffer from the notching effect found in projection structures made by other techniques. Additional deposited layers, tooling, and process steps are not required, as compared with conventional fabrication procedures. The present approach is compatible with the use of alternating phase-shifted masks, an important advantage that permits improved resolution and a reduction in the width of the pole tip.
In accordance with the invention, a method for depositing a projection structure comprises the steps of furnishing a substrate having a top surface, thereafter applying a negative photoresist overlying the substrate, and positioning a mask overlying the substrate and lying in a mask plane generally parallel to the top surface. The mask is a xe2x80x9cnegativexe2x80x9d mask which is opaque in a region defining a location where the projection structure is to be deposited. The method further includes thereafter exposing the negative photoresist through the mask to produce an exposed negative photoresist, thereafter baking and developing the exposed negative photoresist to produce an exposed-and-etched negative photoresist, and thereafter depositing the projection structure through the exposed and etched negative photoresist.
In a preferred application, the substrate is a portion of the magnetic read-write head, built up through the complete read head and the first pole piece and coil windings of the write head. The deposited projection structure comprises a flared portion and a projection extending from the flared portion, deposited upon the substrate. This projection structure includes a pole tip of the write portion of the magnetic read/write head. In this application, the deposited structure is a ferromagnetic material such as an alloy of nickel and iron.
An important embodiment includes the use of a phase-shifted mask, and preferably an alternating phase-shifted mask. The phase-shifted mask may not be used with a positive photoresist to produce the feature geometry required for pole tip definition.
The origin of the notching effect that leads to a degraded structure of conventional pole tip structures has been traced to the effect of light that is reflected from topographical features on the top surface of the substrate during the exposure of the conventionally utilized positive photoresist through the positive mask. This reflected light exposes the positive photoresist in the areas adjacent to and outside of the desired pole-tip profile. Upon developing the positive photoresist, the profile of the sides of the positive photoresist that define the sides of the pole tip after metal deposition are not smooth and parallel, as is desired. Instead, the sides of the positive photoresist are irregular, particularly near the point where the pole tip flares outwardly to the full width of the pole. This irregularity is translated into the deposited pole tip, and is the cause of the undesirable notching effect. Efforts to suppress the reflected light from the top surface of the substrate require additional layers or steps.
In the present approach, by contrast, the result of using a negative mask and a negative photoresist, rather than a positive mask and a positive photoresist, is that any light reflected from topography on the top surface of the substrate is reflected into a volume of the photoresist that is exposed in any event through the transparent portions of the negative mask. The reflected light is thus present, but it does no harm and in fact aids in assuring that the negative photoresist is fully exposed. Accordingly, the notching phenomenon is avoided, and a more perfectly defined projection structure is produced.
The present invention thus provides a more precisely defined projection structure, such as the preferred pole tip and pole, as compared with a conventionally fabricated projection structure. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.